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In this paper experimental dependence of gap voltage collapse during vacuum breakdown on gap geometry and expanding plasma dynamics is investigated by breakdown development simulations. It is shown that experimentally observed differences in voltage fall time between a uniform field gap and a point cathode/plane anode gap is due to different perveances that these two gap configurations have during breakdown. For a point anode/plane cathode gap the braking of the cathode plasma emissive surface is responsible for much longer voltage collapse times. A large scatter in voltage fall time data is explained by the scatter in expansion velocity of the cathode plasma, which is caused by dependence of cathode plasma expansion velocity on the stochastic parameters of an initial cathode microplasma.

The formation of volumetric nanogratings in fused silica by femtosecond laser pulses are shown to afford new opportunities for manipulating the physical shape and tailoring the optical properties of the modification zone by harnessing unconventional beam shapes. The nanograting assembly was observed to rigorously follow the beam elongation effects induced with conical-shaped phase fronts, permitting a scaling up of the writing volume. Detailed optical characterization of birefringence, dichroism, and scattering loss pointed to flexible new ways to tune the macroscopic optical properties, with advantages in decoupling the induced phase retardation from the modification thickness by controlling the conical phase front angle. Further insights into an unexpected asymmetric response from Gaussian beams modified with concave and convex phase fronts have been provided by nonlinear propagation simulations of the shaped-laser light.

Filament arrays were inscribed off-axis in the core of standard single-mode telecommunication fiber, using femtosecond laser pulses. The flexible line-by-line writing formed uniform, parallel filaments, permitting Bragg grating sensing of the photoelastic response from inside of the narrow grating plane. Active monitoring of the Bragg resonance wavelength while driving a lateral fiber tip displacement directly informed on the fiber mechanics when coupled with opto-mechanical modelling. Overlaying of parallel and orthogonal gratings further provided a strongly contrasting azimuthal sensitivity, which paves the way for multi-dimensional displacement sensing with improved precision.

We demonstrate the hybrid integration of an O-band vertical-cavity surface-emitting laser (VCSEL) onto a silicon photonic chip using a grating coupler that is optimized to simultaneously provide feedback to maintain the single emission polarization and efficient in-plane coupling. The grating coupler was fabricated on silicon-on-insulator using a standard silicon photonics foundry process, and integrated with a commercially available VCSEL. A transparent VCSEL submount was fabricated with femtosecond laser templating and chemical etching to simplify the passive and active alignment steps. A record-high VCSEL-to-chip coupling efficiency of -5 dB was obtained at a bias current of 2.5 mA. The slope efficiency and output power are competitive with microcavity hybrid silicon lasers. The results show the feasibility of VCSELs as low threshold current on-chip sources for silicon photonics.